Re: [PATCH 07/15] PCI: endpoint: Add EPC DMA channel delegation hooks

On Fri, Mar 13, 2026 at 01:49:57AM +0900, Koichiro Den wrote:
> Add EPC ops and core wrappers to delegate and undelegate controller-owned
> DMA channels.
>
> The exported DMA helper needs more than a passive "delegated" bitmap:
> it must be able to reserve channels away from local users, let the
> backend perform controller-specific setup (e.g. prevent the EP from
> racing to ack the completion interrupt for delegated channels), and
> later hand the channels back as a matched lifetime operation.
>
> Signed-off-by: Koichiro Den <[email protected]>
> ---
>  drivers/pci/endpoint/pci-epc-core.c | 84 +++++++++++++++++++++++++++++
>  include/linux/pci-epc.h             | 19 +++++++
>  2 files changed, 103 insertions(+)
>
> diff --git a/drivers/pci/endpoint/pci-epc-core.c b/drivers/pci/endpoint/pci-epc-core.c
> index dc6d6ab4ea1e..892f7ccbd236 100644
> --- a/drivers/pci/endpoint/pci-epc-core.c
> +++ b/drivers/pci/endpoint/pci-epc-core.c
> @@ -197,6 +197,90 @@ int pci_epc_get_aux_resources(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
>  }
>  EXPORT_SYMBOL_GPL(pci_epc_get_aux_resources);
>
> +/**
> + * pci_epc_delegate_dma_channels() - reserve EPC-owned DMA channels
> + * @epc: EPC device
> + * @func_no: function number
> + * @vfunc_no: virtual function number
> + * @dir: DMA channel direction
> + * @req_chans: number of channels requested
> + * @chan_ids: output array of delegated channel IDs
> + * @max_chans: capacity of @chan_ids in entries
> + *
> + * Return:
> + *   * > 0: number of channels delegated
> + *   * -EOPNOTSUPP: backend does not support DMA delegation
> + *   * other -errno on failure
> + */
> +int pci_epc_delegate_dma_channels(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
> +				  enum pci_epc_aux_dma_dir dir,
> +				  u32 req_chans, int *chan_ids, u32 max_chans)

Use bit mask should be simple, bit 0 for channel 0, bit 1 for channel 1
...

Frank
> +{
> +	int ret;
> +
> +	if (!epc || !epc->ops)
> +		return -EINVAL;
> +
> +	if (!pci_epc_function_is_valid(epc, func_no, vfunc_no))
> +		return -EINVAL;
> +
> +	if (!req_chans || !chan_ids || !max_chans)
> +		return -EINVAL;
> +
> +	if (!epc->ops->delegate_dma_channels)
> +		return -EOPNOTSUPP;
> +
> +	mutex_lock(&epc->lock);
> +	ret = epc->ops->delegate_dma_channels(epc, func_no, vfunc_no, dir,
> +					      req_chans, chan_ids, max_chans);
> +	mutex_unlock(&epc->lock);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(pci_epc_delegate_dma_channels);
> +
> +/**
> + * pci_epc_undelegate_dma_channels() - release previously delegated channels
> + * @epc: EPC device
> + * @func_no: function number
> + * @vfunc_no: virtual function number
> + * @dir: DMA channel direction
> + * @chan_ids: array of delegated channel IDs
> + * @num_chans: number of entries in @chan_ids
> + *
> + * Return: 0 on success, negative errno otherwise.
> + */
> +int pci_epc_undelegate_dma_channels(struct pci_epc *epc, u8 func_no,
> +				    u8 vfunc_no,
> +				    enum pci_epc_aux_dma_dir dir,
> +				    const int *chan_ids, u32 num_chans)
> +{
> +	int ret;
> +
> +	if (!epc || !epc->ops)
> +		return -EINVAL;
> +
> +	if (!pci_epc_function_is_valid(epc, func_no, vfunc_no))
> +		return -EINVAL;
> +
> +	if (!num_chans)
> +		return 0;
> +
> +	if (!chan_ids)
> +		return -EINVAL;
> +
> +	if (!epc->ops->undelegate_dma_channels)
> +		return -EOPNOTSUPP;
> +
> +	mutex_lock(&epc->lock);
> +	ret = epc->ops->undelegate_dma_channels(epc, func_no, vfunc_no, dir,
> +						chan_ids, num_chans);
> +	mutex_unlock(&epc->lock);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(pci_epc_undelegate_dma_channels);
> +
>  /**
>   * pci_epc_stop() - stop the PCI link
>   * @epc: the link of the EPC device that has to be stopped
> diff --git a/include/linux/pci-epc.h b/include/linux/pci-epc.h
> index 7dd2e4d5d952..db8623b84c56 100644
> --- a/include/linux/pci-epc.h
> +++ b/include/linux/pci-epc.h
> @@ -142,6 +142,8 @@ struct pci_epc_aux_resource {
>   * @stop: ops to stop the PCI link
>   * @get_features: ops to get the features supported by the EPC
>   * @get_aux_resources: ops to retrieve controller-owned auxiliary resources
> + * @delegate_dma_channels: reserve controller-owned DMA channels for peer use
> + * @undelegate_dma_channels: release previously delegated DMA channels
>   * @owner: the module owner containing the ops
>   */
>  struct pci_epc_ops {
> @@ -176,6 +178,16 @@ struct pci_epc_ops {
>  	int	(*get_aux_resources)(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
>  				     struct pci_epc_aux_resource *resources,
>  				     int num_resources);
> +	int	(*delegate_dma_channels)(struct pci_epc *epc, u8 func_no,
> +					 u8 vfunc_no,
> +					 enum pci_epc_aux_dma_dir dir,
> +					 u32 req_chans, int *chan_ids,
> +					 u32 max_chans);
> +	int	(*undelegate_dma_channels)(struct pci_epc *epc, u8 func_no,
> +					   u8 vfunc_no,
> +					   enum pci_epc_aux_dma_dir dir,
> +					   const int *chan_ids,
> +					   u32 num_chans);
>  	struct module *owner;
>  };
>
> @@ -403,6 +415,13 @@ const struct pci_epc_features *pci_epc_get_features(struct pci_epc *epc,
>  int pci_epc_get_aux_resources(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
>  			      struct pci_epc_aux_resource *resources,
>  			      int num_resources);
> +int pci_epc_delegate_dma_channels(struct pci_epc *epc, u8 func_no,
> +				  u8 vfunc_no, enum pci_epc_aux_dma_dir dir,
> +				  u32 req_chans, int *chan_ids, u32 max_chans);
> +int pci_epc_undelegate_dma_channels(struct pci_epc *epc, u8 func_no,
> +				    u8 vfunc_no,
> +				    enum pci_epc_aux_dma_dir dir,
> +				    const int *chan_ids, u32 num_chans);
>  enum pci_barno
>  pci_epc_get_first_free_bar(const struct pci_epc_features *epc_features);
>  enum pci_barno pci_epc_get_next_free_bar(const struct pci_epc_features
> --
> 2.51.0
>